Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this disclosure and are not admitted to be prior art by inclusion in this section.
An x-ray system typically includes an x-ray tube and a detector. The x-ray tube emits radiation, such as x-rays, toward an object. The object is positioned between the x-ray tube and the detector. The radiation typically passes through the object and impinges on the detector. As radiation passes through the object, internal structures of the object cause spatial variances in the radiation received at the detector. The detector then generates data based on the detected radiation, and the system translates the radiation variances into an image, which may be used to evaluate the internal structure of the object, such as a patient in a medical imaging procedure or an inanimate object in an inspection scan.
The x-ray tube includes a cathode and an anode. X-rays are produced in x-ray tubes by applying an electrical current to a filament positioned within the cathode to cause electrons to be emitted from the cathode by thermionic emission. In a vacuum, the electrons accelerate towards and then impinge upon the anode. When the electrons collide with a target on the anode, some of the energy is emitted as x-rays, and the majority of the energy is released as heat. The area on the anode in which the electrons collide is generally known as the focal spot. Because of high temperatures generated when the electron beam strikes the target, specifically the focal spot, the anode can include features to distribute the heat generated at the focal spot on the target, such as rotating a disc-shaped anode target at a high rotational speed. A rotating anode typically includes the disc-shaped anode target, which is rotated by an induction motor via a bearing assembly. Due to the close proximity of the bearing assembly to heat sources of the anode and cathode, the bearing assembly typically operates at high temperatures (e.g., exceeding 200° C.). The combination of the high temperature and high rotational speed of the anode places stringent demands on the bearing assembly.
In addition, the x-ray tube may also be used in a computed tomography (CT) scanner, which includes a gantry that rotates both the x-ray tube and the detector to generate various images of the object at different angles. The gravitational (G) forces imposed by higher gantry speeds and higher anode rotational speeds used in CT scanners can produce additional stresses on the bearing assembly.
Conventional bearing assemblies include tool steel ball bearings and tool steel raceways positioned within the vacuum region and uses lubrication by a solid lubricant, such as silver (Ag) or lead (Pb). Wear and loss of the silver from the bearing contact region increases acoustic noise and can slow down the rotor during operation. In addition, the ball bearings and raceways have limited contact surface areas, which lead to poor thermal conductivity. As a result, new bearing solutions are needed for improved performance under the stringent operating conditions of x-ray tubes in next generation x-ray systems. The technology (systems, devices, and methods) described herein provides bearing solutions with improved performance over conventional bearing assemblies.